Generally, a device for detecting force or moment applied on a working point detects stress-strain produced by the application of the force or moment, thereby to indirectly detect force or moment. Detection of stress-strain is made by providing sensors such as strain gauges on respective portions of a strain generative body and producing a stress-strain in response to the application of force or moment to measure changes in, e.g., resistance values, etc. of those sensors. For instance, where a strain gauge is used as the sensor, stress-strain appears in the form of resistance changes of the strain gauge.
However, the problems with conventional force detector and moment detector are as follows:
First problem is that the device becomes complicated in structure and becomes large-sized. Namely, since a stress sensor such as a strain gauge must be stuck onto a body which is an object in which a stress-strain is caused (hereinafter such a body is referred to as a strain generative body), it is difficult to allow the device to be small-sized. Particularly, in the case of detecting forces and moments in regard to respective directions of three dimensions, it is required to construct a strain generative body in three dimensions to arrange a plurality of strain gauges in three dimensions, so that the structure of the device becomes extremely complicated.
Second problem is that such a conventional device is not suitable for mass production and becomes costly. It is very difficult to conduct the above-mentioned work for sticking strain gauges onto a strain generative body of complicated structure in accordance with a manufacturing line having good efficiency.
Third problem is that measurement accuracy is low. This is because there is a limit in the accuracy of a conventional stress sensor such as a strain gauge, thus failing to make a high precision measurement.
Fourth problem is that complicated computation is required for detecting a force or moment in a specified direction. For example, in the case of arranging strain gauges in three dimensions to independently detect six quantities of forces exerted or applied in respective axial directions and moments exerted or applied about respective axes on the basis of respective outputs thereof, respectively, a complicated computation is required. Since strain gauges respond to given six quantities, respectively, it is required for measuring a specific quantity to perform such a computation to cancel other five quantities.